Gold nanorod particles are nanoparticles of gold with a rod shape (bar-like shape) and show absorption at two wavelength ranges in a visible light range (ca. 520 nm) and a near-infrared range (ca. 900 nm). These are derived from surface plasmon resonance in short axis direction and long axis direction respectively, and the absorption at the near-infrared range is inherent to the gold nanorod particles. Furthermore, the absorbed optical energy is converted into heat, which is called as “photothermal effect”. Since the transparency of biological material is higher in the near-infrared range, it is anticipated that the gold nanorod particles will find application in bio-imaging on the basis of intense near-infrared absorption capability thereof, photothermal treatment by use of heat generation, and the like, for example (see Non-Patent Documents 1, 2).
In recent years, Au—Ag core-shell nanorod particles are reported in which gold nanorod particles are cores and silver shell layers coat their surface (see Non-Patent Document 3). By way of coating with silver, absorption range of the particles shifts to blue. Furthermore, since silver-specific plasmon absorption is larger than that of gold, the photothermal effect can be enhanced by coating with silver.
Non-Patent Document 1: Drug Deliv. Syst., Vol. 24, No. 3, p. 260.
Non-Patent Document 2: J. Am. Chem. Soc., Vol. 130, No. 32, pp. 10643-10647.
Non-Patent Document 3: Chem. Lett., Vol. 38, No. 1, pp. 60-61.